Discriminating circuits for dualpurpose trunks



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ATTORNEY I I l l l I l lI ROBERT W. HUTTON .VON

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Filed Nov. 5, 1951 R. W. HUTTON DISCRIMINATING CIRCUITS FOR DUAL-PURPOSE TRUNKS lO Sheets-Sheet 8 June 29, 1954 R. w. HUTTON DISCRIMINATING CIRCUITS FOR DUAL-PURPOSE TRUNKS Filed NOV. 5, 1951 l0 Sheets-Sheet 9 .TOOmN mnEDOo @z EOOZ- June 29, 1954 R. w. HUTTON 2,682,577

DISCRIMINATING CIRCUITS FOR DUAL-PURPOSE TRUNKS Filed Nov. 5, 1951 1o sheets-sheet 1o m Ei Patented `lune 29, 1954 DISCRIMINATING CIRCUITS Fon DUAL- PURPOSE TRUNKS Robert W. Hutton, Chicago, Ill., assgnor, by mesne assignments, to International Telephone and Telegraph Corporation, a corporation of Maryland Application November 5, 1951, serial No. 254,843

7 Claims.

This invention relates to discriminating circuits for dual-purpose trunks such as are used in telephone switching systems. Its general object is to provide new and improved discriminating terminal circuits for trunks of the indicated character which permit a single trunk group to eiectively replace two trunk groups.

One specific object is to provide terminal circuits for a trunk interconnecting two automatic telephone exchanges and so arranged that a call thereover from the rst exchange may be directed to either of two locations in the second exchange according to the designation dialed to reach the trunk in the rst exchange.

Another specic object is to provide terminal circuits for an interexchange trunk for causing a connection over the trunk to be controlled in the second exchange according to the class of the call, as whether from a subscriber or from a toll operator.

A further object is to provide terminal circuits of the indicated character for trunks using derived dialing circuits, including composited and simplexed trunks.

A feature of one embodiment of the invention is that the required directional or class-indicating information is passed to the second exchange according to the polarity employed in the rst exchange to energize the dialing circuit, and that the polarity used in the. second exchange to relay answered supervision back to the rst exchange is selected to agree with polarity applied to the dialing circuit in the rst exchange.

A related further feature concerns changing the polarity of the dialing circuit, following its closure on seizure of the trunk in the rst ex change, without causing a false operation of the incoming dialing relay in the second exchange.

A feature of a second embodiment is that the required directional or class information is passed to the second exchange accordance to whether or not a voice-frequency signal is transmitted over the talking path, as distinct from a signal over the dialing circuit.

Other objects and features of the invention will become apparent as the description progresses.

I. GENERAL DESCRIPTION It has been chosen to illustrate the invention as embodied in a group of exchanges including two automatic telephone exchanges located comparatively close together, rendering it economical to provide service between them on a. local basis, and to issuea single directory covering both ex- CII changes. The switching apparatus must therefore be so arranged that the telephone numbers are the same when called from either exchange.

In the chosen illustration, a toll board is located in the same building which houses the second of the noted automatic exchanges. The calls in either direction between the two exchanges are handled over a single group of trunks, and the length of these trunks is assumed to be great enough to render it economical to use them as two-way trunks, rather than as two one-way groups. y

With the two exchanges and the `toll board bearing respective single-digit designations (such as 3, 8, and 0, respectively), the single group of interexchange trunks can handle all calls from the rst exchange only if it is arranged that a trunk of the` group is seized in the first exchange responsive to dialing the designation of either the second exchange or the toll board, and if the call be selectively directed in the second exchange according to the designation dialed in the rst exchange.

Since some distinction is required in practice to be made in the handling of a call from the second exchange to the first, according to whether the call is from the toll board or from a line of the second exchange, a single group of trunks can be used for calls in the concerned direction only if it is arranged that apparatus in the first exchange responds selectively according to whether the call is a toll call or a call from a subscriber of the second exchange.

IA. The drawings extension of talking connections between these various exchanges;

Figs. 10 and l1 show modications of the circuit apparatus of Figs. 2 to 9; and

Figs. l2 to 14, located on the same sheet of drawings as Figs. 9, part 2, show the way in which the sheets of drawings on which Figs. l

to 11 are drawn, Should be arranged in order to be understood best.

Referring to Figs. 4 to 9, Fig. 4, parts l and 2, show in circuit detail the switchboard apparatus of exchange A;

Figs. 5 and6, taken together, disclose in circuit detail the apparatus of the trunk coupler of exchange A;

Figs. '7 and 8, taken together, disclose in circuit detail the apparatus of the trunk coupler of exchange B; and

Fig. 9, parts l and 2, disclose in circuit detail the switchboard apparatus of exchange B.

Referring to Figs. l0 and l1, Fig. `il), replacing Fig. 5, shows in circuit detail a second embodiment of the trunk coupler of `exchange A; and

Fig. l1, replacing Fig. 8, shows in circuit detail a second embodiment of the trunk coupler of exchange B.

Fig. l shows three exchanges A, B, and C, with a toll board TB associated with exchange B. Calls among these exchanges and the toll board are handled over the indicated trunk groups, comprising'two-way group B393, one-way groups SQE- and-E-, a two-way group between TB and C, and a one-way group from C to B. The calls over the ytrunk groups shown connected to C are assumed to be exclusively toll calls, handled` through the usual toll board (not shown) in exchange C.

Referring now to Fig. 2, the switchboard apparatus of exchange A is of the crossbar type disclosed in the application of Bellamy` and Bowser, Serial No. 85,292, led April 24, i949, for a Primary-Secondary-Spread Crossbar Telephone System. It includes a main distributing frame, M. D. through which lines and trunks are connected with the switchboard apparatus; linelink frames A, B, C, and D, of which line-link frames A and B are shown at 256A and iiB; a block-link frame shown at 2,51; and a trunk coupler frame shown at 252.

The generalpurpose of the switchingvapparatus of exchange A is to interconnect the subscriber lines of exchange A with each other, and with the inter-exchange trunk line as desired, as well as to interconnect the inter-exchange trunk line to subscribers as desired.

As hereinbefore pointed out, the invention is embodied in a system as disclosed in the noted Bellamy and Bowser application. The line-link frames A and Band the blocl-link frame with the exception of the incoming block coupler and the trunk coupler is as disclosed and described in the noted application. Incoming block coupler l-I and-trunk coupler 205i will be described in detail hereinafter.

IBl. Local call-exchange A Brieiiy, the operations involved in extending a call from the subscriber at station Si on calling line Esato the-subscriber at station S2 on called line 2H), is as follows:

IThe subscriber at -station Sli removes his receiver and dials the directory number of station S2, comprising the .listed initial digit 3, followed by the listed hundreds, tens, units, and stations digits of the number. As-pointed out in the noted application, line controller switches iUGBA and HMA operate to associate-line controller IZGSA with line-link primary switch SMA, at which the calling line terminates. A line-link, such as line-link y202A and an originating trunk such as originating trunk ZSA are tested over respective conductors '2152A and 4 H3A. If found idle, the line controller matches an idle path from the calling line to an idle block coupler, such as local block coupler S68-L. Thereafter, the line controller causes the primary and secondary switches SilliAand 9813A to effect the mechanical selection of the matched line-link 202A and causes the associated holdmagnet (not shown) to close the appropriate stackup of contact members in these switches -to extend--thecalling line to local block coupler 50G-L. The line controller switches and the line controller are now released, leaving calling line 2GB connected to Vlocal block coupler 52m-L by way of line-link; 262A, originating trunk 293A, and block coupler jumper 264.

As describedin the noted application, following the dialing of the directory number of a local subscriber, local block coupler 50G-L causes block. controller switch |580 to associate block controller iGU with primary switch i303 which is associated with block coupler 50c-L over conductors in group 255. At the same time, block coupler 5mi-L is associated with block controller i606 over the conductors in group 22 i, and block translator i830 receives the registered digit information over conductor groups H, T, U, and ST.

The block translator thereupon determines the line-link frame which serves the called line (linelink frame Bl) and transmits thereto (over conductors in group 223B) translated digit information indicating the primary switch (BBBB) which serves the called line, and indicates the speciiic vertical appearance of the called line on that primary switch. The line controller IEQBB causes the line controller switches IMDB and HUUB to position themselves, according to the switchboard location of `the called line. The line-links (such as 262B) are now tested over respective conductors in group2i2B and this testing information is imparted to bloclrcontroller 169% over respective conductorsin group 222B'. The sleeve conductor 2l IB of the called line alle is extended to block controller |530 over conductors in group 222B permitting the block controller to test the called line as to its busy or idle condition. If the line tests idle, the block controller matches an idle path thereto over a block-link such as blocklink 2HE, a terminating trunk such as terminating trunkrillB and a line-link such as line-link 202B. These block links and terminating trunks and the called `line has been determined, the

block controller extendsthe connection from the associated block `coupler to the called line by operating blockprimary switch i365, block secondary switch i409, line-link secondary switch 900B and line-linky primary switch 899B. rhe local block coupler applies ringing current to signal-the calledstation S2. lThe items of common apparatus are now returned to common use leaving the connection intact between the calling line and thev called line.

When the call has been answered. the subscribers at stations Si and S2 may converse. When both subscribers have replaced their receivers, the existing connection is broken at each of the switches 800A, 900A, 13M, Hlii, 989B and B.

IB2. Exchange A calls exchange B When the subscriberv at station Si on lineii desires to call the subscriber at exchangefB, he

Si removes his receiver and dials the directory number of the desired subscriber. This directory number includes an initial digit 8` which is assigned specically to lines of exchange B.

As previously described when the receiver is removed at the calling station SI, the calling line is extended to an idle block coupler such as local block coupler 500-L.

When the initial digit 8 is dialed, a connection is immediately completed over a wire in initial digit group ID for calling in outgoing controller |700 for setting it with specific regards to the trunk group leading to the called exchange B. Block controller |600 and block controller switches |500, together with outgoing controller |100, cause block-link primary switch |300 and secondary switch |400 to extend the connection to an idle trunk in the called vtrunk group.

If block-link 206 and the outgoing trunks such as outgoing trunks 2020-8 and 2020-0 are idle (as shown by a test made over respective conductors 22T-8 and 22T-0), block controller |600 causes switches |300 and |400 to extend the connection from block coupler 500-L to trunk 2020-8 or 2020-0, depending on the initial digit dialed.

The calling line is thereb-y extended through block coupler 500-L to trunk coupler 205| on trunk coupler frame 252. Since the call is to a local subscriber at exchange B, (indicated by the initial digit 8) the trunk coupler 205| repeats the pulses of the remaining digits over the trunk line to the apparatus in exchange B, as will hereinafter be described.

The connection established by the calling line to the outgoing trunk is released responsive to operations occurring in the trunk coupler 205| when the receiver is subsequently replaced at the calling station SI.

When exchange A is called from exchange B, the call reaches exchange A over a two-way trunk line such as 2003. This trunk line is extended through jumpers 2082 and 2084 to trunk coupler 205|. Trunk coupler 205| extends the connection to block coupler |500-I over incoming trunk 2085 and jumpers 204' and 2084.

Block coupler |500-I is similar to local block coupler v500-L except that it preferably does not apply dial tone upon being taken for use nor does it have any provisions for receiving any initial digit.

Following the seizure of incoming block coupler |500-I, the call may be directed only to local subscribers in exchange A by the dialing of the appropriate directory number (block coupler |500-I does not have an initial digit register therefore calls incoming over incoming trunk 2085 can not reach a trunk level). The connection is extended to the called line 2|0 and station S2 thereon in the manner previously described for a call originated at calling station Sl. The operation of incoming block coupler |500-I will be described in greater detail hereinafter.

Referring now to Fig. 3 it will be observed that the switchboard apparatus of exchange B is generally similar to that of exchange A as shown in Fig. 2. However, portions of the common apparatus have been omitted but their operation is as described with reference to corresponding apparatus of Fig. 2.

ICl. Local call-exchange B The subscriber at station S| on line |200 may call the subscriber at station S2 on line |2|0 in the manner previously described with reference 6` to the subscriber at station SI on line 200 calling the subscriber station S2 on line 2 |0.

IC2. Exchange B calls exchange A v equipment of the block-link frame, shown at |25l, causes block-primary and block-secondary switches |300 and |400 to associate the concerned block coupler with an idle outgoing trunk, such as outgoing trunk 9020-3, over conductors in group |205. Block coupler |500-L is now connected to trunk coupler 2052 through jumper 902 |-3. Trunk coupler 2052 seizes the associated trunk coupler 205| of exchange A over trunk line 2093 and the associated main distributing frame jumpers 2082 and 2059.

The calling subscriber SI at exchange B thereupon dials the directory number of the desired subscriber in exchange A. As hereinbefore pointed out, incoming coupler |500-I does not have an initial digit register, therefore, all calls from exchange B to exchange A can be only to local subscribers in exchange A.

IDl. Emchanye B calls toll board TB If the subscriber SI on line |200 desires to call the operator at the toll board, a block coupler such as local block coupler |500-L is associated with the calling line as previously described. The dialing of the initial digit 0 causes the common equipment to associate the calling block coupler with outgoing trunk 9020-0 over conductors in group |205 and through block primary and secondary switches |300 and |400. The connection is extended through jumper 902| to trunk coupler 900| which is extended to the toll board over jumper 2022. The calling station Si on line |200 may converse with the toll operator at the toll board.

Trunk couplers 900|, 9053 and 2054 are oneway trunks assumed to be similar to the outgoing repeater OR-I shown in Fig. 8 of the drawings of Patent No. 2,427,650, issued to Pier Bakker for a Multi-Exchange Community Autolmatic Telephone System. Trunk OR-I of the noted Bakker patent is a two-Way trunk between a manual and automatic exchange, however, it will be assumed that trunk couplers 900|, 9053, and 2054 are similar to the one-way portion of the noted trunk repeater.

m2. Exchange A calls tzz board TB Incoming calls from exchange A to the toll board TB reach the switchboard apparatus of exchange B through a main frame jumper such l IE. Toll call to exchange A or exchange B On calls from exchange C to exchange B, the

`connection is extended through main frame coming trunk 2085-3.

jumper 2055 tol trunk coupler frame |252.. The

connection thereupon reaches trunkcoupler 205I` and is further extended to an incoming coupler such as incoming coupler 350D-I, The call may then be extended to exchange A if the initial digit 3 is dialed or it may be extended to a local subscriber in exchange B by dialing the desired directory number.

The operator at the toll board may originate an outgoing call or a terminating call by seizing trunk coupler 9053 which is associated with coupler S500-I over an incoming trunk such as in- The operator may thereupon dial a digit 3 to reach exchange A or dial the directory number of any desired subscriber.

Trunk coupler 900|, 9053, and 2054 are oneway trunk repeaters and as hereinbefore described, may be as described and illustrated in the noted Pier Bakker application.

II. DETAILED DESCRIPTION The invention having been described generally, a detailed description will now be given with reference to Figs. 4 through 9.

Fig. 4, parts l and 2, Fig. 5 and Fig. 6 disclose switchboard apparatus located in exchange A while Fig. '7, Fig. 8, and Fig. 9, parts l and 2, disclose switchboard apparatus of exchange B.

IIA. Calls from exchange A to archange B A detailed description of the operation of the system in extending talking connections from a local subscriber in exchange A to another local subscriber at exchange B and in extending a 'talking connection from a local subscriber in exchange A to the operator at exchange B, will now be given with particular reference to Figs. 4 through 9.

IlAl. Station S1 on line 200 calls station S2 on Zine 1210 The subscriber at station SI on line 200 in exchange A, to call the subscriber at station S2 on line IZIQ in exchange B, removes his receiver, waits for a dial tone from a local block coupler, such as block coupler 500-L, and then dials the trunk digit indexing exchange B, followed by the directory number of station S2 on line I2 I 0.

As described in the noted Bellamy and Bowser application, when the receiver is removed at calling station SI, calling line 200 is associated with an idle local block coupler such as local coupler 50B-L through the operation of the line controller switches and the line controlleron the line-link frame containing the calling line. Station SI on line 200 is connected to local block coupler 50G-L through main frame jumper 20I, through contacts on line-link primary switch SoU-A, over a line-link such as line-link 202-A, through contacts on line-link secondary switch .lt-A, over originating trunk S-A and jumper 204.

As hereinbefore pointed out, block coupler 5cc-L is generally as described and disclosed in the noted Bellamy and Bowser application. Therefore, the dialing of the initial digit (8) indexing an outgoing trunk to be used in reaching the desired local subscriber in exchange, B causes the common apparatus of the switchboard at exchange A to extend the connection from block coupler 500-L over the tip, ring, and sleeve conductors of groups 205, through block-link primary switch I300, over a block-link such as block-link 20B, and through contacts on blocklink secondary switch |400- to outgoing trunk 2020-8 extending to f trunk coupler 2I15I-y overk cable K-2020-8 and jumper 202I-8. The calling line loop is thereby extended to trunk coupler 205 I.

In order for the calling line to be extended to trunk coupler 205 I, the common apparatus inthe outgoing controller tests the sleeve conductor of outgoing trunk 2020-8 and upon finding idleindicating battery from idle-indicating resistor 6I2 through back contacts 4 and I of relays 603 and 605, respectively, of trunk coupler 205|, associates the calling line with the trunk coupler.

The line loop being closed across the tip and ring conductors extending to trunk coupler 205I, operates outgoing line relay B04 through back contacts 5 and 6 of incoming cut-through relay E03, the A and B windings of repeat coil SI5, back contacts I and 2 of incoming cut-through relay 603, and break contacts I and 2 of outgoing supervisory relay 501.

Operation of outgoing line relay 504 causes ground potential to be placed to the winding of outgoing hold relay 605 through back contacts l of relay 603. Relay 505 operates and at its contacts 2 prepares a seizure circuit for seizing the trunk coupler at exchange B.

Operation of outgoing hold relay 505 removes the idle-indicating battery potential from the sleeve conductor of the calling line and replaces it with ground potential. Conta-cts 4 of outgoing hold relay 505 extend ground potential to the Winding of toll discriminating cut-o relay |60I, operating it; contacts 5 place a shunt around, the winding of relay 603 and around its associated rectier H504; and contacts 6 extend negative battery'potential from current-limiting resistor SIS through back contacts 3 of toll control relay C08, back contacts 2 of outgoing toll discriminating auxiliary relay Iiil, over wire IBM through make contacts 2 of outgoing relay 004, over wire E40 through the upper winding of incoming line relay 600, and over wires 163i and |630 through the C and D windings of repeat coil SI5 to trunk wires Ll and L2 extending to exchange B.

Negative battery potential from current-limiting resistor 5I3 reaches exchange Bv over trunk wires LI and L2, and is extended through the C and D windings of repeat coil H5 over wire E73!! to incoming toll discriminating relay i102 and its associated rectiier i104. The polarity 0f rectifier ITM. is such that it offers negligible resistance to current flow from negative battery potential appearing across the LI and L2 conductors of the simplex line. This negative battery potential is therefore extended through rectier |704 to ground potential through the winding of incoming line relay '100 over wire I'I3I, and over wire 140 through back contacts 2 of relays "IM and 101, causing incoming line relay to operate.

The incoming line relay 600 of Fig. 6 and incoming line relay 700 of Fig. 'l have double wound coils with their windings. diierentially connected. The lower windings are connected to ground potential through the associated variable resistors Mil and H4. The setting of these resistors are such that their resistance equals the impedance of the line. Therefore, if battery potential through resistor 6I3 is placed on wire 640, an equal amount of current ilow passes through both windings of relay 500 preventing its operation as the iiux generated in the windings is equal and opposite. However, incoming line relay 109 has its lower winding shunted `by ground potential from contacts 2 of relay 'I0'Iy hence battery potential appearing on wire I'I3-I energizes the upper winding of relay 100 only and operates it.

Operation of incoming line relay 100 causes ground potential to be extended to the winding of incoming repeat relay operating it. Contacts 2 of relay 10| extend ground potential to the winding of incoming hold relay 102, operating it.

Operation of incoming hold relay 102 causes ground potential to be extended to the winding of incoming cut-through relay 103 through back contacts 3 of outgoing hold relay 105. Contacts 2 of incoming hold relay 102 prepare an operate circuit for series relay 105.

Incoming cut-through relay 103 operates and at its contacts 4 remove the idle-indicating battery from the sleeve conductor of outgoing trunk 9020-3; contacts I and 2 and 5 and `6, together with make contacts of relay 10| place the windings of the polarized relay 108 (incoming supervisory) across the tip and ring conductors of incoming trunk 2085| extending to incoming coupler Z500-I over conductors in cable K-2005-|; contacts 3 place ground potential on the sleeve conductor of incoming trunk 2085| and contacts 1 open the operate circuit of relay |10|.

Incoming couplers |500-I and Z500-I are incoming couplers similar to incoming coupler 500-I of the noted Bellamy and Bowser application. However, in both noted incoming couplers, the initial digit register and the reverting call relay have been omitted. The numbering of the relays in coupler |500-I is similar to the numbering of the corresponding relays in coupler 500-I except for the additional prei-lx 1. In coupler Z500-I, the relay numbers are prefixed with the digit 2. Discriminating relay |526 has been added to coupler |500-I and differential relay 2528 and toll relay 2529 have been added to coupler 25004. The operation of these added relays will be described in full hereinafter.

The tip and ring conductors of incoming trunk 2085-I are bridged by the windings of relay 108 in series with current-limitingl resistor '||8 and the A and B windings of repeat coil 1|5. This loop across the tip and ring conductors of incoming trunk 2035-! is extended through break contacts and 2 of back-bridge relay 2502, the winding of differential relay 2528 and the winding of line relay 2503 of incoming coupler 2500-I to battery and ground potentials.

Differential relay 2528 having a double wound coil with the windings connected in opposing relationship will not operate as the current flow through both windings is equal and opposite. However, line relay 2503 operates from the current flowing and, as described in the noted Bellamy and Bowser application, at its contacts and 2 operates release relay 2505 and series relay 2504 preparing incoming coupler 2500-I for receiving the dial pulses constituting the digits of the directory number of the Vdesired subscriber S2 on line |2|0.

As hereinbefore pointed out with reference to the noted Bellamy and Bowser application, the dialing of an initial digit assigned an outgoing desired subscriber at station S2 on line |2|0 by the calling subscriber Sl on line 200 causes outgoing line relay 604 of trunk coupler 205| to restore and reoperate according to the dial rpulses constituting the directory number of the desired subscriber as the block coupler has switched--V through,

Contacts 2 of outgoing line relay S04 transfer wire 040 from battery potential to ground potential on each restoratiomthereby generating battery and ground potential pulses. These battery and ground potential pulses are extended to incoming line relay '|00 of trunk coupler 2052 over the noted path and over trunk line wires L| and L2. At the same time, ground potential is extended through back contacts of relay 004 and through make contacts 2 of outgoing hold relay 505 operating series relay 605 of trunk coupler 205|. Contacts and 2 of relay |305 shunt the A and B windings of repeat coil SI5 in order to improve dialing.

Incoming line relay 100 of trunk coupler 2052 responds to the battery and ground pulses received from trunk coupler '205| by restoring and reoperating to repeat these pulses to the Winding of incoming repeat relay 10| causing it to restore and reoperate accordingly.

Line relay 10| of trunk coupler 2052, restoring and operating, open and close the line loop across the tip and ring conductors of incoming trunk 2085| extending to incoming trunk coupler 2500-1. At the same time,y ground potential is extended through back contacts 2 of relay 10| and through make contacts 2 of incoming hold relay 102 to the winding-of series relay 100. Series relay 100 operates and at its contacts and 2 shunt the inductive windings A and B of repeat coil 1 |5 to improve dialing; at its contacts 3 shunt break contacts of count relay 1||; and at its make contacts 4 operates countrelay 1| The opening and closing of the line loop across the tip and ring conductors of incoming trunk 2085-I, extending to incoming coupler Z500-I, causes line relay 2053 to restore and reoperate accordingly. On each restoration of line relay 2503, ground potential through contacts is extended through make contacts 3 of release relay 2505 to wire 2550 extending to sequence register SE. Make contacts 2 open and close the operate circuit of series relay 2504 causing it to restore and remain restored until the completion of the dialing of each digit. These pulses of ground on wire 2550 are extended through break contacts of sequence register SE to battery potential through the winding of hundreds register HR. Hundreds register HR, as described in the noted Bellamy and Bowser application operates step by step according to the number of pulses in the rst digit.

. At its make contacts, hundreds register I-IR pretrunk level causes the concerned block coupler to l switch-through, extending the calling line loop across the tip and ring conductors of the outgoing trunk. Therefore, as the calling line loop is opened and closed by the dial, the loop across the tip and ring conductors of outgoing trunk 2020-8 is opened and closed.

The dialing of the directory number of the pares an operate circuit for sequence register SE responsive to the reoperation of series relay '2504 at the end of each digit.

On completion of the dialing of the irst digit, series relay 2504 reoperates and at its contacts 5 place ground potential through the noted make contacts of the hundreds register HR, through break contacts 5 of ring cut-off relay 2501 to battery potential through the Winding of sequence register SE1, advancing, it to its next position.

On the dialing of the second digit of the directory number of the desired subscriber, restoration of line relay 2503 restores series relay 2504 removing the ground potential from the winding of sequence register SE. At its back contacts line relay 2503 delivers ground potential pulses to wire 2560 extending to the tens register TR (not shown) through break contacts 2 and make contact of sequence register SE. On completion of the dialing of each digit, register` SE advances to its next position thereby causing the pulses of ground potential on wire 2550 to be extended to the register corresponding to the digit dialed.

When the dialing of the directory number of -the desired subscriber S2 on line I2 0 is completed,

as described in thenoted Bellamy and Bowser application, the tip, ring, and sleeve conductors of incoming block coupler Z500-I is extended through conductors in group 205|, over a block- Alink such as block-link |206 to a terminating trunk such as terminating trunk |201 extending to line-link secondary switch 1000B. The common control apparatus thereafter extends the connection over a line-linx such as line-link |202B, through secondary switch |900B and primary switch |800B to line |2|0, and through main frame jumper |209 to the called station S2 on line |2|0. The called station is now signalled in the normal manner and the calling station on calling line 200 of exchange A is extended to station S2 on the called line |2|0 of exchange B.

When the called station S2 on line E2 i0 answers the call, back-bridge relay250l operates from the called line loop closure and at its contacts and 2 reverses the tip and ring conductors extending to trunk coupler 2052. This reversed battery and ground potentials from incoming coupler 2500-1 causes incoming supervisory relay '|08 of trunk coupler 2052 to operate as relay is a polarized relay. At its contacts I, relay '|00' extends ground potential to the winding of incoming supervisory auxiliary relay 's', operating it. At its contacts 2, relay 101 removes ground potential from wire '|40 and replaces it with negative battery potential. This negative battery potential is extended over trunk line LI and L2 to trunk coupler 205| of exchange A to operate incoming line relay 000. Both upper windings of relays 600 and '|00 are shunted by battery potential andthe lower windings are connected across battery and ground po- .f

tentials. The lower windings of both line relays are thereby energized, operating both relays. Contacts on incoming relay '600 operate repeat relay 60| which at its contacts 2 operate incoming hold relay 602. Contacts 2 of incoming hold relay 002 extend ground potential through make contacts 3 of outgoing hold relay 005 to the winding of outgoingV supervisory relay lill'l', operating it. At its contacts and 2, relay 007 reverses the battery and ground potentials on the tip and ring conductors of incoming coupler |500-I furnishing reverse battery supervision.

The established connection is cleared out responsive to the opening of the line loop across the tip and ring conductors of incoming trunk 2085| by the replacing ofthe receiver of the calling subscriber. The concerned block couplers in exchanges A and B and the concerned trunk couplers are returned to normal use again, each supplying an idle-indicating battery po tential to the sleeve conductor, indicating their idle condition.

IIA2. Station S1 on Zin-e 200 calls the operator at toll board TB The local subscriber at exchange A (station Sl on line 200) to reach the operator at station B, dials the digit 0 and automatically is cutthrough to the toll board. The operation of the r12 system in handling'the calls from a local subscriber in exchange A to an operator at exchange B `will now be described with particular reference to Figs. 4 through 9.

As hereinbefore pointed out, the removal of the receiver at station SI on line 200 associates the calling line with a block coupler such as block coupler B-L over a line-link such as line-link 202A and an originating trunk such as originating trunk 203A. Dialing of an initial digit O causes the apparatus in exchange A to extend the calling line to an outgoing trunk such as 25120-6 through block-primary switch |300 and block-secondary switch |000 over a block-link such as block-link 206. The calling line is further extended over conductors in cable K-2020-8 through trunk jumpers 202|-0 to the tip, ring, and sleeve conductors of trunk coupler 205|. As hereinbefore pointed out, the common control equipment of exchange A will extend the calling line to outgoing trunk 2020-0 responsive to the dialing of the digit 0 only if the sleeve conductor of such an outgoing trunk is idle. This idle-indicating battery is supplied through current-limiting resistor 6|2 of trunk coupler 205|. The tip and ring conductors of outgoing cable K-2020-0 is extended to ground and battery potentials rthrough the winding of outgoing line relay 00-4 through contacts and 2, and 5 and 0 of incoming cut-through relay 503, through the A and B windings of repeat coil '6|5, and through back contacts and 2 of outgoing supervisory relay '1. The ring conductor is also extended through the winding of high resistance outgoing toll discriminating relay |602.

The high resistance winding of outgoing toll discriminating relay |602 being in the series with the windings of outgoing line relay 604 limits the current owing through the calling line loop to a value which prevents the operation of relay 604 but causes outgoing toll discriminating relay |602 to operate.

Contacts of outgoing toll discriminating relay |602 operate outgoing toll discriminating auxiliary relay |600 and contacts 2 of relay |602 operate outgoing hold relay 606 through back contacts l of incoming cut-through relay 603. Contacts 2 of outgoing toll discriminating auxiliary relay |600 extends positive battery potential through current-limiting resistor |605 to wire |60| extending to make contacts 6 of relay 605.

Operation of outgoing hold relay 605, causes ground potential to be extended through its make contacts 2 to operate series relay 606; causes its contacts 4 to extend ground potential to toll discriminating cut-off relay ||60|, operating it; causes its contacts 5 to shunt the incoming toll discriminating relay |603 and its associated rectifier |600; and causes its contacts 6 to extend the noted positive battery potential to make contacts 2 of line relay 604 in preparation for seizing trunk coupler 2052 of exchange B.

Series relay 606, at its contacts l and 2, shunt the A and B windings of repeat coil 6|5 placing the tip and ring conductors of outgoing trunk 2020-0 directly across the windings of outgoing line relay 604.

Toll discriminating cut-oit relay |60| operates responsive to the closing of contacts 4 oi outgoing hold relay 605. Its contacts shunt the high resistance Winding of outgoing toll discriminating relay |602, causing it to restore. The closing of contacts I, shunting the high resistance winding of relay |602, permits the current ow through the windings of outgoing line relay 604 to reach an operating value thereby causing outgoing line relay 604 to operate.

Operation of outgoing line relay 604, causes contacts to extend a locking ground potential on wire |040 to hold outgoing hold relay `|505 and toll discriminating cut-off relay |60| operated. Series relay 6016 releases responsive to the operation of outgoing line relay 604 as ground potential is removed from back contacts of relay 604. The tip and ring conductors of the calling line is again extended through the A and B windings of the repeat coil ||5.

Contacts 2 of outgoing line relay 005i extend the noted positive battery potential on wire |64| to wire B40 extending to the windings of incoming line relay 600. This battery potential is extended through the upper winding of relay 000 over wire |63I, through make contacts 5 of outgoing hold relay 605, over wire |030 and through the C and D windings of repeat coil SI5 to trunk coupler 2052 in exchange B over trunk lines L| and L2.

This positive battery potential is extended through the C and D windings of repeat coil 1|5 to wire |130 extending to incoming toll discrimilniing relay |102 and its associated rectifier Rectifier |104 is connected in shunt of incoming toll discriminating relay |102 in such a man ner that it oers negligible resistance to negative battery potential and innite resistance to positive battery potential. Since the battery potential appearing on wire |130 is positive, rectier |104 directs the current low through the winding of incoming toll discriminating relay |102, operating it. Relay |102 locks operated through its make contacts and at its contacts 3 prepare trunk coupler 2052 tofurnish the proper battery polarity for answer supervision. Positive battery potential from current-limiting resistor |605 is further extended over wire |13|, through the Winding of incoming line relay 100 and over wire 140 to ground potential at con* tacts 2 of incoming supervisory auxiliary relay 101 through break contacts 2 of outgoing line relay 104.

As hereinbefore pointed out, line relays 600 and 100 of Figs. 6 and '7 have tandem-wound diierentially-connected relay coils. Associated with each relay is a current-limiting resistor such as 5M and 'H4 and each are initially adjustedto match the impedance of the trunk line extending between the two exchanges. With thisadjustment correctly made, the current flow through the upper and lower windings of relay 500 is equal and opposite and relay B00 does not operate. However, ground potential on wire 140 shunts the lower winding of relay 100 thereby permitting the winding to be eiTectiVe, causing relay 100 to operate.

As previously described, operation of incoming line relay 100 causes relays '|02 and '|03 to operate. Contacts on these relays bridge the tip and ring conductors of incoming trunk 2085-! and extend this closed line loop over incoming trunk 2085| of cable K-2085-I to incoming coupler 2500-1. This loop is extended through the windings of line relay 2503 and through the windings of differential relay 25|8 to battery and ground potentials. Current ow over the line loop causes the line relay 2503 of incoming coupler 2500-1 to operate. Since relay 2528 is a diiTerentially-connected relay and equal amounts of current now through each winding, relay 2528 does not operate.

v14 Make contacts y2 of line relay 2503 extend ground potential to the winding of series relay 2504 operating it and at its make contacts tential on the sleeve conductor of incoming trunk 2085| to render this trunk coupler busy to outgoing calls.

In its normal condition, condenser 1|1 is fully charged from battery and ground potential through current-limiting resistor 1| 6. Operation of incoming hold relay 102 causes its contacts 4 toextend the full charge on condenser 1|1 through back contacts -9 of outgoing hold relay 105 and through make contacts 2 of operated incoming toll discriminating relay |102 to battery potential through the winding of toll control relay 1|0.

Relay 1| 0 operates from the current ilowing from the discharging condenser 1|1. When the condenser is fully discharged, relay 1|0 restores. Make contacts on toll control relay 1|0 place ground potential through break contacts 4 of series relay 106 to the ring conductor of the incoming trunk 2085| extending to incoming trunk coupler 2500-1 over cable K-2085-l. This ground potential is placed on the ring conductor only momentarily as relay 1|0 remains operated only for the time duration of the discharge of condenser 1|1. f

This momentary pulse of ground potential is extended over the ring conductor of incoming' trunk 2085| tofincoming coupler 2500-I shunting the upper winding of differential relay 2520 and line relay 2503 thereby causing the current flow through the lower winding of the differential relay to be eifective, operating relay 2528. Ground potential from contacts of diierential relay 2528 is extended to the winding of toll relay 2529.

Toll relay 2529 operates and locks to ground potential on wire |5|9 through its make contacts and at its make contacts 2 extends ground potential from wire 2520 (as described and illustrated in the noted former application, the corresponding wire is at ground potential) to wire ID|0 extending to the outgoing controller |100 of Fig. 6 of the noted Bellamy and Bowser application. This ground potential on initial digit wire ID|0 causes the common apparatus of exchange B to extend the connection through a primary and secondary switch on the block-link frame to an outgoing trunk such as an outgoing trunk 3020-0 extending to trunk coupler 000| As hereinbefore pointed out, trunk co-upler 900| is similar to the trunk coupler of the noted Pier Bakker application and the seizure of this trunk coupler by the switch-through operations of block coupler Z500-I causes the toll operator to be signalled in the normal manner.

When the toll operator answers the call, the line loop across the tip and ring conductors extending to the toll board is closed, thereby operating back-bridge relay 2502 which at its contacts and 2 reverse the tip and ring conductors of incoming trunk 20854. This battery reversal on the tip and ring conductors causes incoming supervisory relay 108, a polarized relay, to operate and extend ground potential to the winding of relay 101, operating it. Incoming supervisory auxiliary `relay 101 at its contacts l shunt the lower winding of incoming toll discriminating relay |102 which remains operated through energization of Yits upper winding and at its contacts 2 remove ground potential from Wire 100 and replace it with positive battery potential through current-limiting resistor 1|3. This posi tive battery potential is thereby transmitted over trunk line LI and L2 extending to exchange A and through the winding of incoming line relay 001i to'positive battery 'from current-limiting resistor i605. As previously pointed out, battery potential of the same polarity on both sides of the upper windings of the line relays shunt the upper `windings and energizes the lower windings. Thereforarelaysf and` 100 are operated from the current flow through their lower windings.

Relay B00, at its contacts, extends ground potential to the Winding of yincoming repeat relay of trunk coupler 205|', operating it. Contacts on relay 60| extend ground potential to the winding of incoming holdrelay 602, operating it. Make contacts 2 of incoming hold relay S02 extend groundpotential to the winding of outgoing supervisory relay 001, operating it. Contacts and 2 of outgoing supervisory relay G01 providel the calling stationSl on line 200 with answered supervision. The calling party 5| on line 200 of exchange vA,may converse with the toll operator at exchange B.

On completion of the conversation between the calling subscriber in exchange A and the operator the connection will be broken and the equipment used will be returned to common use in prepa-ration for another call.

IIB. Calls from exchange B to exchange A A detailed description of the operation of the system in extending a talking connection from a local subscriber in exchange B to another local subscriber in exchange A or in extending a talking connection from the operator at exchange B to a local subscriber in exchange A will now be given with particular reference to Figs. 4 through 9.

HB1.. StationSion Zine 1200 calls station S2 on line 210 The subscriber at station SI on line |200 in exchange B, to call the subscriber at station S2 on line 2|0 in exchange A, removes the receiver,

waits for the dial tone from a local block coupler such as block coupler |500-L, and then dials the trunk digit indexing exchangeA, followed by the directory number of station S2 on line 2i0.

As hereinbefore noted, the removal of the receiver at a calling station SI causes the calling line to be associated with an idle local block coupler through the operation of line controller switches and the line controller on the line-link frame containing the calling line. Station Si is connected to a local block coupler such as coupler |500-L through main frame jumper ii, through contacts sets on line-link primary switch 800A, over a line-link such as line-link |202A, through contacts sets on line-link secondary switch 900A, and over an originating trunk such as originating trunk |203A and its associated `iumper |204.

As hereinbefore noted, the dialing of an initial digit "3 by a subscriber in exchange B causes the concerned block coupler to seize an outgoing trunk extending to exchange A. Therefore, the common apparatus of the switchboard at exchange B (shown in part in Fig. 3) extend the connection from block coupler H500-L over the tip, ring, and sleeve conductors of group |205, through contact sets on block-link primary switch 2300A, over a block-link such as block-link |200, and through contact sets on block-link secondary switch |300A to outgoing trunk 0020-3 and jumper 902|.-3. The connection is thereby extended from the calling subscriber to trunk coupler 2052 over outgoing trunk 0920-3 In order for the calling line to seize trunk coupler 2052, the common apparatus in the outgoing controller not shown) tests the sleeve conductor of outgoing trunk 0020-3 and if it iinds idle-indicating battery from idle-indicating resistor 1|2 (Fig. 7) causes block coupler L5M-L to switch-through and seize trunk coupler 2052.

The line loop being closed across battery and ground potential through the windings of outgoing line relay 104 through break contacts i and 2 of outgoing supervisory relay 100, through back contacts and 2, and 5 and S of incoming cutthrough relay 103, and through the A and B windings of repeat coil 1|5, operates relays 10d.

Contacts of outgoing line relay 104 extend ground potential through back contacts 1 of incoming cut-through relay 103 and back contacts i of outgoing hold relay |05 to the winding of outgoing toll discriminating relay llli. Relay |10! operates and at its contacts 2 extend its operating ground potential to the winding of outgoing hold relay 105, operating it. Contacts 2 of relay 104 prepare a seizure circuit for seizing trunk coupler 205| in exchange A.

Operation of outgoing hold relay 105 transfers the sleeve conductor of outgoing trunk 9020-3 from idle-indicating battery potential to ground potential through the lower winding of outgoing sleeve detector relay thereby guarding the concerned coupler against seizure. Contacts 5 prepare an operate circuit for series relay 106; make contacts 4 close a locking circuit for relays and |10I; make contacts 2 extend ground potential to wire |132; contacts 1 place a shunt around the Winding of incoming toll discriminating relay |102 and around its associated rectiiier |104; contacts 8 extend negative battery potential from current-limiting resistor 'H3 through make contacts 4 of operated outgoing toll discriminating relay |10|, make contacts 2 of outgoing line relay 104, over `wire through the upper winding of incoming line relay 100, over wire |1|3, contacts 1 of relay 105, wire |130, and through the C and D windings of repeat coil l|5 to exchange A over trunk wires Ll and L2; and break contacts 9 open the operate circuit oi toll control relay 1|0.

Negative battery potential from current-limiting resistor 1|3 reaches exchange A over trunk wires Ll and L2 and is extended through the C and D windings of repeat coil @I5 to wire |030 extending to the winding of incoming toll discriminating relay |630 and its associated resistor i604. The polarity of rectifier |604 is such that it oiiers negligible resistance to the flow of current from the negative battery potential. This negative battery potential is extended through rectifier |604, through the winding of incoming line relay 600, over wire |631, through back contacts 2 of outgoing line relay 000 and through back contacts 2 of incoming supervisory auxiliary relay .609 to ground potential. Current iiow over this noted path causes incoming line relay 600 to operate.

When trunk coupler 205| is seized by trunk coupler 2052 with negative battery'potential over the LI and L2 conductors, incoming line relay '|00 remains in an unoperated condition due to the equal amounts of current flowing through each of its windings, but incoming line relay G operates as its lower winding is shunted by ground potential through variable resistor |4 and ground potential through back contacts 2 of incoming supervisory auxiliary relay 500. Operation of incoming line relay 500 causes its contacts to place ground potential to the winding of incoming repeat relay 50|,v operating it.y Contacts 2 of relay 50| extend ground po- -tential to the winding of incoming hold relay 502,` operating it. Contacts 2 of incoming hold relay 502 extend ground potential through back contacts 3 of outgoing hold relay 005 tothe winding of incoming cut-through relay 503 and prepare an operating circuit for series relay 505.

Relay 003 operates and at its contacts 4 remove the idle-indicating battery from the sleeve conductor of outgoing trunk 2020-0; contacts I 'and 2, and contacts 5 and 5 of relay 505, together with make contacts I of incoming repeat relay 00| place the `windings of incoming supervisory relay 6|0 (polar relay) in series with currentlimiting resistor 6|0 across the tip and ring conductors of incoming trunk 2085, extending to incoming coupler |500-I over the conductors in cable K-2085; contacts 3 and 4 extend battery potential through resistor 5|2 to the sleeve conductor extending to incoming coupler |500-I; and contacts open the operate circuit of outgoingA hold relay E05. As previously pointed out, incoming coupler |500-I is similar to incoming coupler 500-1 of the noted Bellamy and Bowser application. The initial digit register IDR, and the reverting call relay have been omitted while discriminating relay |525 has been added. The numbering of the relays is similar to the numbering in the noted application except the numeral two is prefixed pervisory relay 5|0 is placed in series with resistor SIS across the tip and ring conductors of incoming trunk 2085 extending to incoming coupler |500-I. This closed loop across the tip and ring conductors is extended through back contacts I and 2 of switch-through relay (not r shown) and through back contacts I and 2 of back-bridge relay |502 to battery and ground potentials through the windings of line relay |503. Current flowing through this closed line loop causes line relay |503 to operate.

Contacts I of line relay |503, as described in the noted Bellamy and Bowser application, extends ground potential to the Winding of release relay |505, operating it. Make contacts of release relay |505 extend battery potential from current-limiting resistor 5|2 of trunk coupler 205| through break contacts 2 of time pick-up relay |5|3 to the upper winding of discriminating relay |5|5. Discriminating relay-|525, however, does not operate at this time as it is shunted by ground potential from break contacts I of units register UR.

Make contacts 2 of line relay |503 extend ground potential to the winding of series relay |504, operating it. Contacts 5 of series relay |504 prepare an operate path for sequence counter SE, following the dialing of the rst digit.

After seizure of incoming coupler |500-I by trunk coupler 205| from the calling subscriber S| on line |200, the'hundreds, tens, units and station digits of the desired subscriber S2 on line 2|0 is dialed. As theline loop is opened and closed by the calling subscriber dial contacts, outgoing line relay` |04 of trunk coupler 2052 follows these pulses and at its contacts Iy extend battery and ground potential pulses to wire 140 extending toy incoming line relay '100. These pulses of battery and ground potential are transmitted over trunk lines LI and L2 to ground potential at back contacts 2 of incoming supervisory auxiliary relay 509.l

Incoming line relay 500 restores and reoperates according to the pulses of battery land ground potential and extends corresponding pulses of ground to the winding of incoming repeat relay 00| causing it to restore and reopcrate.v The restoration and reoperation of relay y60| causes its make contacts to open and close the line loop across the tip and ring conductors extending to incoming coupler |500-I. Line rev lay |503 follows this opening and closing of the line loop and at its make contacts extend pulses of ground potential through back contacts I of relay |503, through make contacts 3 of releasey relay |505, and through break contacts of sequence counter SE over wire |550 to the winding of hundreds register HR, causing it to advance to a position corresponding to the value of the digit dialed. During the dialing of each digit, pulses of ground potential are extended through make contacts ofrelay |503 to the winding df release relay |505 holding it operated.

As described in the noted Bellamy and Bowser application, duringthe dialing of the rst digit, series relay |504 restores and on completion vof the dialing of the first digit, reoperates and remains operated until the next digit isdialed. Ground potential from make contacts 5 of series relay |504 is extended through make contacts I of hundreds register HR and through back contacts 5 of ring cut-off relayy |501 to the winding of sequence counter SE, causing it to advance one step.

Counter SE operates on completion of the dialing of the 'first digit and transfers wire |550 fromthe winding of hundreds register HR. to the winding of tens register'TR. Subsequent digits dialed cause sequence counter SE to advance on the completion of the dialing of each digit and transfer the pulsing wire `|550 to the corresponding register.

Referring now to trunk coupler 2052 of Figs. '7 and 8, it will be noted that, following its seizure, relays 104, |05, and Il0| areoperated. As described in the noted Bellamy and Bowser application, seizure of trunk coupler 2052 or any outgoing trunk from any block coupler is kaccomplished by switching-through operations. For the'slcw-release time of the release relays such as relay 2505, ground potential remains on the sleeve conductor of the coupler extending to the concerned outgoing trunk. This ground potential is therefore shunting the lower winding of relay for a duration of time possibly greater than the inter-digit time interval. In order that the trunk coupler maydiscriminate between a toll and a local call by detecting the presence of ground potential on the sleeve conductor, the

ifi? discrimination must bedelayed until the noted svvitch-tl'iroughv ground potential disappears.

As previously pointed out, if the call to a local subscriber in exchange A was originated by a toll operator at the toll board, aV toll coupler such. as incoming coupler 3500-1 projects ground potential ahead on the sleeve conductor. If the call were originated by a local subscriber, the holding ground` for the concerned primary and secondary switches would be supplied from. the concerned trunk coupler.Y Trunk coupler 2052 must, therefore, be arranged to delay the discrimination operationsuntil the: start of the second digit of the directory number. Ther operation of trunk coupler 2052 in discriminating between a local. and a toll call will now be described.

Referring noW to Figs. 7 and. 8, it will be observed that outgoing toll discriminating relay |10I. is locked operated over two paths. One locking path is from battery potential through the lower Winding of relay |10I, through its make contacts 2 or 3 to ground potential through make contacts of outgoing line relay 104. The other locking path is from battery potential through the upper Winding of relay |10 l, through its make contacts I to ground potential onI wire |132 through break contacts` I of count. relay II I.

During the dialingof. the irstv digitof the directory number of. station S2 on line 21|) of exchange` A, outgoing line relay 1:04 restores and reoperates according to the digit dialed. On each restoration of relay 104, the locking path for the lower winding of relay I'IOI is opened. However, series relay 106 operates andv remains operated during the dialing of each. digit and atv its contacts` 5 extends ground: potential from wire |132 tothe upper Winding of relay I-I-0l maintaining it operated. At its contacts 6, relay '|06 extends ground potential to: the Winding ci count relay II-I.; and at its contacts and 2, shunt the A and B windings of repeat coil 1I5 to improve dialing..

Count relay 1I operates and locks. through its contacts 2 to ground potential on wire |132. At it scontactsy relay 'I I opens the locking circuit of the upper Winding of relay IL10-I...

When the line. relay '|04 reoperates.. upon completion of the dialing of the first.. digit its make contacts I close the locking circuit for the lower Winding of relay |101. and. at itshreak. contactsv I, restoreseries relay 106..

After. completion of. the. dialing of thev first digit of the directory number, the. sleeve conductor S of outgoing trunk 9020-3 has battery potential on it, if thecall is fromA alocal subscriber, or has ground. potential on it, if the call is froman operator.

Since the call was originated by a local subscriber, current,V ow from ground potential through the` lower winding of relay |100- to the noted. battery potential on-y theA sleeve conductor of. trunk0020-f,` operates relay |100. Relay |100 locks operated to. ground potential on locking wire I'I.32v and. at its contacts I shunt contacts I of count relay 'II-I and contacts 3 of series relay T06.

Relay |`|0I remains locked operated throughout the duration of the call and at its. contacts 4, maintain negative battery potential on wire 100 extending to exchange A.

Therefore, on a call from. a localY subscriber in exchange B to a local subscriber in exchange A, trunk coupler 205| is seized by negative battery potentialover wiresLI and L2. and the' digits are 2Q dialed withpulses of. this negative battery potential.

ReferringV new to Fig, 4, operation 0I units register UR.` removes the shunting` ground poten.- tial from the Winding of discriminating, relay i526. permitting it to operate from battery potential. through current-limiting resistor E I2. oi? trunk coupler 205|'. Dis-criminating relay |523. locks operated through its lower Winding and make contacts 2, to ground potential enz Wire |543. Contacts Iv of relay- |526 complete.- the operate path ofr time pick-up relay ISI-3 thereby permitting permanent timing and conversation timing to take place in coupler` |500-I.

Oncompletion. of the dialing of the directory number of the called: subscriber S2 on line 2I0, the common equipment at exchange` A operates, as described. and. disclosed in the noted Bellamy andv Bowser'application, to signal the called sta.- tion S2.

When the called party answers, the closing of the called line operates back-bridge relay |502, which at its contacts I: and` 2, reverse the battery and ground potentialacross the tip and ring conductors extending from trunk coupler 205|. This battery reversal causes incoming supervisory relay 6I0 tov operate. Atv its contacts. 2, relay 6|.0 extends ground potential from. makeA contacts 2 of incoming hold relay 002 andthrough back contacts 2 of outgoing hold relay 605 tothe Winding of incoming supervisory auxiliary relay 609013- erating it.

At its make contacts I, relay-i609 places-a shunt across` incoming toll discriminating. rela-y |603 and its associatedrectiiier |004, and. at its` make contacts 2, removes ground potential from. wire EN and replaces it with negative battery potential through current-limiting resistor 61a.. This battery potential is extendedl over wireszLI and L2 to the winding of incoming relay 100; thereby operating it as the upper windings of both. incoming line relay 600- and 1.00 areshunted by battery potential from. current-limiting re.- sistor 5|f3 in trunk coupler 205| and currentlimiting resistor 143mtrunk coupler 20.52..

Contacts on incoming line relay 1.00. extend ground potential to the winding of incoming, repeat. relay 'iii-i., operating it. Contacts 2 of in.- coming repeat relay 'ICM extend. ground potential to the winding of incoming hold relay 102 operating it. Make. contacts 3 of incoming hold rela-y |02 extend ground potential through make contact. 6 of outgoing hold relay 105 to the winding of outgoing supervisory relay 109, operating it. Contacts I and. 2. of outgoing supervisory relay 109, reverse the battery and ground. potentials across the tip and ring conductors of outgoing trunk 3020-3,v extending to the` calling line.

The calling subscriber SI. on calling l-i-ne |200 may now converse with the called station S2 on called line 2 I 0.

On completion of the conversation, disconnect by the calling party, perm-its the apparatus` used in the talking connection to restore to normal in preparation for another call.

HB2. Toll bom-d TB calls stationA S2 on line 210 Referring now to Fig.v 3 of the drawings it will be observed that the operator at the toll board may seize an incoming toll coupler 3500-1 over an incoming trunk 2085-3 and its associated trunk coupler 9053, and that exchange C may reach an incoming toll coupler such as toll coupler 35013-1. over. an incoming trunk such as incoming 

